I'm working in a project that uses"blade solidity ratio", or "rotor solidity", the problem is, there are several articles which defines the equation in a different way changing in the section of the Radius analysis. I found 3 equations that I will describe below:
$$1. \frac{Nc}{2πR}$$ $$2. \frac{Nc}{2R}$$ $$3. \frac{Nc}{R}$$ N=Number of Blades, c= Chord Length, R= Radius of the rotor
Which one is correct or there is some case where each of this equation is applied? Thanks.